1. Field of the Invention
The present invention relates to a method and apparatus for water jet peening, and more particularly to a method and apparatus for water jet peening that is preferably applicable to a nuclear power plant.
2. Description of the Related Art
It is known that a residual stress mitigation method is available to give compressive residual stress to the surface of a structural member of a nuclear power plant or the like by subjecting such a structural member by applying water jet peening.
A water jet peening method described in JP-2010-276491-A subjects the outer surface of a bottom mounted instrument piping to water jet peening by disposing a jet nozzle, which discharges a jet of high-pressure water, at the bottom of a reactor pressure vessel and rotating the jet nozzle, which is discharging a jet of high-pressure water, around the bottom mounted instrument piping. In this manner, compressive residual stress is given to the outer surface of the bottom mounted instrument piping.
A water jet peening method for giving compressive residual stress to the inner surface of piping is described in JP-2008-14447-A. This water jet peening method inserts a working device in piping with a jet nozzle into a piping, moves the working device within the piping, and allows the jet nozzle to discharge a jet of high-pressure water toward the inner surface of a welding area of the piping. Hence, compressive residual stress is given to the inner surface of the welding area.
A water jet peening method to be applied in a piping is described in JP-2002-200528-A. In order to subject the inner surface of a welding area formed inner side of a piping to water jet peening, a jet nozzle is inserted into the piping from one end of the piping, and the one end of the piping is sealed with a tube plug while the other end of the piping is sealed with a tube plug or with a valve. Water is then filled into a sealed area in the piping. Eventually, the inner surface of the welding area formed on the piping is subjected to water jet peening by allowing the jet nozzle in the water to discharge a jet of high-pressure water. When the jet of high-pressure water is discharged, air existing in the sealed area is expelled outside through a pipe connected to the tube plug.